KR20220154776A - Sn-based plated steel sheet - Google Patents

Abstract

[Problem] To provide a Sn-based plated steel sheet capable of exhibiting superior corrosion resistance, yellowing resistance, coating film adhesion, and yellowing blackening resistance without using a chromate coating.
[Solution Means] The Sn-based plated steel sheet of the present invention includes a steel sheet, a Sn-based plating layer positioned on at least one side of the steel sheet, and a film layer positioned on the Sn-based plating layer, wherein the Sn-based plating layer is Sn 1.0 g/m ² to 15.0 g/m ² per side in terms of metal Sn, the coating layer contains zirconium oxide, and the content of the zirconium oxide is 1.0 mg/m 2 per side in terms of metal Zr. m ² to 10.0 mg/m ² , and the zirconium oxide includes zirconium oxide having an amorphous structure, and a crystalline layer containing zirconium oxide having a crystalline structure as a main component is present on the upper layer of the zirconium oxide having an amorphous structure. do.

Description

Sn-based plated steel sheet

The present invention relates to a Sn-based coated steel sheet.

Tin (Sn)-plated steel sheet is also well known as "tin plate" and is widely used for cans such as beverage cans and food cans, and other uses. This is because Sn is safe to the human body and is a beautiful metal. This Sn-based plated steel sheet is mainly manufactured by an electroplating method. This is due to the fact that the electroplating method is more advantageous than the hot-dip plating method in order to control the amount of Sn, which is a relatively expensive metal, to a minimum necessary amount. The Sn-based plated steel sheet is subjected to a chromate treatment (electrolytic treatment, dipping treatment, etc.) using a solution of hexavalent chromate after plating or after imparting a beautiful metallic luster by heat-melting treatment after the plating, on the Sn-based plated layer. In many cases, a chromate coating is applied. The effect of this chromate film is to prevent yellowing of the external appearance by suppressing surface oxidation of the Sn-based plating layer, to prevent deterioration of coating film adhesion due to cohesive failure of tin oxide in the case of coating and use, and to improve resistance to yellowing and blackening. improvement, etc.

On the other hand, in recent years, because of the heightened awareness of the environment and safety, it is required not only that hexavalent chromium is not contained in final products, but also that chromate treatment itself is not performed. However, as described above, a Sn-based plated steel sheet without a chromate coating has a yellow appearance due to the growth of tin oxide. For this reason, some Sn-based plated steel sheets subjected to a coating treatment in place of the chromate coating have been proposed.

For example, Patent Document 1 below proposes a Sn-based plated steel sheet in which a film containing P and Si is formed by treatment using a solution containing phosphate ions and a silane coupling agent.

In Patent Document 2 below, Sn-based plating in which a film containing Al and P, at least one of Ni, Co, and Cu, and a reactant of a silane coupling agent is formed by treatment using a solution containing aluminum phosphate. A steel plate is suggested.

Patent Literature 3 below proposes a method for producing a Sn-based coated steel sheet without a chromate coating, in which Zn plating is applied on the Sn-based plating and then heat treatment is performed until the Zn-only plating layer disappears.

In Patent Document 4 and Patent Document 5 below, a steel sheet for containers having a chemical conversion coating film containing zirconium, phosphoric acid, phenol resin or the like is proposed.

In Patent Document 6 below, a Sn-based plating layer and a Sn-based chemical conversion layer formed by performing cathodic electrolytic treatment and then anodic electrolytic treatment in an aqueous phosphate solution after forming the Sn-based plating layer, and containing tin oxide and tin phosphate. Plated steel sheets have been proposed. Further, Patent Literature 6 proposes that when forming a film, alternating electrolysis in which cathodic electrolytic treatment and anodic electrolytic treatment may be performed alternately may be performed.

Patent Document 7 below proposes a Sn-based plated steel sheet having a coating containing tin oxide and Zr, Ti, and P.

Japanese Unexamined Patent Publication No. 2004-060052 Japanese Unexamined Patent Publication No. 2011-174172 Japanese Unexamined Patent Publication No. 63-290292 Japanese Unexamined Patent Publication No. 2007-284789 Japanese Unexamined Patent Publication No. 2010-013728 Japanese Unexamined Patent Publication No. 2009-249691 International Publication No. 2015/001598

In the methods proposed in Patent Documents 1 to 7, there is a problem that the corrosion resistance is slightly inferior to that of the chromate-coated tin plate, and there is room for improvement in the corrosion resistance. Therefore, a Sn-based plated steel sheet having not only yellowing resistance, coating film adhesion, and yellowing blackening resistance but also superior corrosion resistance has been desired.

Therefore, the present invention has been made in light of the above problems, and an object of the present invention is a Sn system capable of exhibiting better corrosion resistance, yellowing resistance, coating film adhesion, and yellowing blackening resistance without using a chromate coating. It is to provide galvanized steel sheet.

In order to solve the above problems, as a result of intensive examination by the present inventors, a coating layer containing zirconium oxide is formed on the surface of a Sn-based plated steel sheet, and the distribution of the crystal structure of the zirconium oxide in the coating layer is set to a specific state. Conventionally, It has been found that a Sn-based coated steel sheet having superior corrosion resistance can be realized.

The gist of the present invention completed based on the above findings is as follows.

(1) A steel sheet, a Sn-based plating layer positioned on at least one surface of the steel sheet, and a film layer positioned on the Sn-based plating layer, wherein the Sn-based plating layer has Sn in terms of metal Sn, 1.0 per side. g/m ² to 15.0 g/m ² , the coating layer contains zirconium oxide, and the content of the zirconium oxide is 1.0 mg/m ² to 10.0 mg/m ² per side in terms of metal Zr, The zirconium oxide includes zirconium oxide having an amorphous structure, and a crystalline layer containing zirconium oxide having a crystalline structure as a main component is present on the upper layer of the zirconium oxide having an amorphous structure. Sn-based plated steel sheet.

Here, in the electron beam diffraction pattern, a case where a clear diffraction spot is obtained is determined to be a crystalline structure, and a case where a ring-shaped continuous diffraction pattern is obtained instead of a clear diffraction spot is determined to be an amorphous structure.

(2) The crystalline layer in the coating layer includes the outermost surface portion of the coating layer, and the number of detected spots in the crystalline layer is at least one or more in order from the outermost surface portion in the thickness direction; (1) The Sn-based plated steel sheet described in.

Here, the outermost surface portion means a portion including the outermost surface of the coating layer among the portions obtained by dividing the coating layer into 10 parts in the thickness direction at an arbitrary position of the coating layer, and the number of detection points of the crystalline layer is , In an arbitrary position of the coating layer, the coating layer is divided into 10 equal portions in the thickness direction, and in the electron beam diffraction pattern of the central portion in the thickness direction of each portion divided into 10 equal parts, the number of locations judged to be crystalline structures among the measured 10 locations it means.

(3) The Sn-based plated steel sheet according to (2), wherein the number of detection spots of the crystalline layer is five or less in order from the outermost surface portion in the thickness direction, including the outermost surface portion of the coating layer.

As described above, according to the present invention, it is possible to provide a Sn-based plated steel sheet superior in corrosion resistance, yellowing resistance, coating film adhesion, and yellowing blackening resistance without performing conventional chromate treatment.

Below, preferred embodiments of the present invention will be described in detail.

In this specification, the term "process" is included in the term as long as the intended purpose of the process is achieved not only in an independent process but also in a case where it cannot be clearly distinguished from other processes. In this specification, the term "steel sheet" means a base steel sheet (so-called plated original sheet) for forming a Sn-based plating layer and a coating layer.

Embodiments of the present invention described below relate to cans such as food cans and beverage cans, and Sn-based coated steel sheets widely used elsewhere, and methods for manufacturing such Sn-based coated steel sheets. More specifically, a Sn-based coated steel sheet and a Sn-based coated steel sheet that are further excellent in corrosion resistance (more specifically, corrosion resistance after coating), yellowing resistance, coating film adhesion, and yellowing blackening resistance without performing the conventional chromate treatment. It's about manufacturing methods.

Specifically, the Sn-based plated steel sheet according to the present embodiment includes a steel sheet, a Sn-based plating layer positioned on at least one side of the steel sheet, and a coating layer positioned on the Sn-based plating layer. Here, the Sn-based plating layer contains 1.0 g/m ² to 15.0 g/m ² per side of Sn in terms of metal Sn. In addition, the film layer contains zirconium oxide, and the content of zirconium oxide is 1.0 mg/m ² to 10.0 mg/m ² per side in terms of metal Zr. In addition, zirconium oxide contains zirconium oxide having an amorphous structure, and a crystalline layer containing zirconium oxide having a crystalline structure as a main component exists on the upper layer of the zirconium oxide having an amorphous structure.

Hereinafter, the Sn-based plated steel sheet according to the present embodiment and its manufacturing method will be described in detail.

<About steel plate>

The steel sheet is not particularly defined, and any steel sheet can be used as long as it is a steel sheet used for Sn-based coated steel sheets for general containers. As such a steel plate, low carbon steel, ultra-low carbon steel, etc. are mentioned, for example. Also, the manufacturing method and material of the steel plate are not particularly specified, and for example, a steel plate manufactured through processes such as casting, hot rolling, pickling, cold rolling, annealing, and temper rolling can be used.

<About the Sn-based plating layer>

A Sn-based plating layer is formed on at least one side of the steel sheet as described above. The corrosion resistance of the steel sheet is improved by the Sn-based plating layer. In addition, "Sn-based plating layer" in this specification means not only a Sn-based plating layer of metal Sn alone, but also an alloy of metal Sn and metal Fe, metal Ni, and at least one of trace elements and impurities other than metal Sn (eg For example, Sn-based plating layers containing Fe, Ni, Ca, Mg, Zn, Pb, Co, etc.) are also included.

The Sn-based plating layer contains 1.0 g/m ² to 15.0 g/m ² per side in terms of metal Sn. That is, the amount of deposition per side of the Sn-based plating layer is 1.0 g/m ² to 15.0 g/m ² in terms of the amount of metal Sn (ie, the amount in terms of metal Sn). When the amount of adhesion per side of the Sn-based plating layer is less than 1.0 g/m ² in terms of the amount of metal Sn, the corrosion resistance is poor, which is not preferable. When the amount of adhesion per side of the Sn-based plating layer is 1.0 g/m ² or more in terms of the amount of metal Sn, it is possible to express excellent corrosion resistance. The amount of deposition per side of the Sn-based plating layer, in terms of the amount of metal Sn, is preferably 2.0 g/m ² or more, more preferably 5.0 g/m ² or more. On the other hand, when the amount of deposition per side of the Sn-based plating layer exceeds 15.0 g/m ² in terms of the amount of metal Sn, the effect of improving corrosion resistance by metal Sn is sufficient, and further increase of the layer is undesirable from an economical point of view. Further, when the amount of adhesion per side of the Sn-based plating layer exceeds 15.0 g/m ² in terms of the amount of metal Sn, the coating film adhesion also tends to decrease. When the amount of adhesion per side of the Sn-based plating layer is 15.0 g/m ² or less in terms of the amount of metal Sn, it is possible to achieve both excellent corrosion resistance and coating film adhesion while suppressing an increase in cost. In order to achieve both excellent corrosion resistance and coating film adhesion at low cost, the amount of metal Sn deposited per side of the Sn-based plating layer is preferably 13.0 g/m ² or less, more preferably 10.0 g/m ² or less.

Here, the amount of metal Sn in the Sn-based plating layer (ie, the amount of adhesion per side of the Sn-based plating layer) is a value measured by, for example, the electrolysis method described in JIS G 3303 or the fluorescent X-ray method.

Alternatively, for example, the amount of metal Sn in the Sn-based plating layer can be determined also by the following method. First, a test piece in which no coating layer is formed is prepared. The test piece was immersed in 10% nitric acid to dissolve the Sn-based plating layer, and Sn in the obtained solution was analyzed by ICP (Inductively Coupled Plasma) emission spectrometry (eg, 799ce manufactured by Agilent Technologies, Ar in a carrier gas). is used.). Then, the amount of metal Sn can be determined based on the strength signal obtained by analysis, a calibration curve prepared from solutions of known concentrations, and the formation area of the Sn-based plating layer of the test piece.

Alternatively, in the case of a test piece on which a coating layer is formed, the amount of metal Sn can be obtained by a calibration curve method using GDS (Glow Discharge Spectroscopy), and the method is, for example, as follows. Using a plating sample (reference sample) in which the amount of metal Sn is known, the relationship between the intensity signal of metal Sn in the reference sample and the sputtering rate is determined in advance by GDS, and a calibration curve is prepared. Based on this calibration curve, the amount of metal Sn can be obtained from the strength signal of a test piece having an unknown amount of metal Sn and the sputter rate. Here, the Sn-based plating layer is the portion from the depth at which the Zr intensity signal is 1/2 of the maximum value of the Zr intensity signal to the depth at which the Fe intensity signal is 1/2 of the maximum value of the Fe intensity signal. Defined by

From the point of view of measurement accuracy and rapidity, measurement by a fluorescence X-ray method is preferable industrially.

The method for applying Sn-based plating to the surface of the steel sheet is not particularly specified, but a known electroplating method is preferred. As the electroplating method, an electrolytic method using, for example, an acidic bath such as a well-known sulfuric acid bath, boric fluoride bath, phenolsulfonic acid bath, or methanesulfonic acid bath, or an alkali bath can be used. Alternatively, a melting method in which Sn-based plating is performed by immersing a steel sheet in molten Sn may be used.

Further, after the Sn-based plating, a heat melting treatment may be performed in which the steel sheet having the Sn-based plating layer is heated to 231.9° C. or higher, which is the melting point of Sn. By this heat-melting treatment, the surface of the Sn-based plating layer remains glossy, an alloy layer of Sn and Fe is formed between the Sn-based plating layer and the steel sheet, and corrosion resistance is further improved.

<About the coating layer containing zirconium oxide>

The Sn-based plated steel sheet according to the present embodiment has a film layer containing zirconium oxide on the surface of the Sn-based plating layer formed on the surface of the steel sheet. This zirconium oxide needs to contain zirconium oxide with an amorphous structure and zirconium oxide with a crystalline structure.

When the coating layer contains zirconium oxide of an amorphous structure, the number of grain boundaries serving as a transmission path for corrosion factors such as oxygen and chloride ions is reduced compared to a coating layer containing only zirconium oxide of a crystalline structure. As a result, it becomes difficult for corrosion factors to reach the Sn surface, and the corrosion resistance of the coating layer is improved.

Here, the structure of zirconium oxide is determined by an electron diffraction pattern using a transmission electron microscope. That is, in the electron beam diffraction pattern, a case where a clear diffraction spot was obtained was defined as a crystalline structure, and a case where no diffraction spot was obtained and a ring-shaped continuous diffraction pattern was obtained was defined as an amorphous structure. Specifically, a sample for TEM (Transmission Electron Microscope) observation is prepared by FIB (Focused Ion Beam) at an arbitrary site of the Sn-based plated steel sheet, and an arbitrary film position is beamed By examining a diffraction pattern obtained by diffracting an electron beam with a diameter of 1 nm, the crystal structure can be determined as described above.

Moreover, it is preferable that zirconium oxide of an amorphous structure in this embodiment is contained 50% or more as an amorphous structure ratio in a film layer. In addition, the definition of "amorphous structure ratio" in this embodiment is described later for convenience of description. When the amorphous structure ratio in the coating layer is 50% or more, it becomes possible to further improve the corrosion resistance of the coating layer. The amorphous structure ratio in the film layer is more preferably 60% or more. In addition, the upper limit of the amorphous structure ratio is 90%.

The amorphous structure ratio defined here is a value calculated from the ratio of the location where the amorphous structure was obtained in the coating layer. Specifically, the electron beam diffraction pattern of 10 random locations in the thickness direction is measured at an arbitrary position on the surface of the coating layer. In these measurement results, a case where a ring-shaped continuous diffraction pattern is obtained instead of a clear diffraction spot is judged to be an amorphous structure. Among the total of 10 locations measured in this way, the ratio of the locations where an amorphous structure was obtained was defined as the amorphous structure rate.

Amorphous structure ratio (%) = (Number of sites where amorphous structure was obtained/10) × 100

In addition, it is preferable to measure the number of detection points of the amorphous structure as described above at 3 arbitrary positions in the coating layer, and more preferably at 5 arbitrary positions in the coating layer. In addition, the maximum value of the number of detection points at each measurement position was taken as the number of detection points of an amorphous structure.

In the coating layer according to the present embodiment, a crystalline layer containing zirconium oxide having a crystalline structure as a main component is present in the upper layer of the zirconium oxide having an amorphous structure as described above. This is because, when a Sn-based coated steel sheet is coated and used, when zirconium oxide having a crystalline structure exists on the surface layer side of the Sn-based coated steel sheet, the coating film adhesion is better. Although a monoclinic system is mentioned as a crystal structure of zirconium oxide, other crystal structures, such as a tetragonal crystal and a cubic crystal, may be contained. In addition, the above-mentioned "which has a zirconium oxide which has a crystalline structure as a main component" means that the content of the zirconium oxide which has a crystalline structure in a crystalline layer is 50 mass % or more.

As a mechanism for showing better coating film adhesion with zirconium oxide having a crystalline structure rather than having a zirconium oxide having an amorphous structure on the surface layer side, the contact interface with the coating film increases due to fine irregularities on the crystal plane, and furthermore, the structure is more crystalline than the amorphous structure. Since the structure has more reactivity, it is conceivable that the reactivity with the coating film is high.

In addition, it is preferable that the crystalline layer in the coating layer includes the outermost surface portion of the coating layer, and that the number of detected spots in the crystalline layer is at least one or more in order from the outermost surface portion in the thickness direction. Here, the outermost surface portion means a portion including the outermost surface of the coating layer among the portions obtained by dividing the coating layer into 10 parts in the thickness direction at an arbitrary position of the coating layer. That is, it means that zirconium oxide having a crystalline structure exists on the outermost surface of the Sn-based plated steel sheet. In addition, the number of detected locations of the crystalline layer is determined by dividing the coating layer into 10 equal portions in the thickness direction at an arbitrary position of the coating layer, and in the electron beam diffraction pattern of the central portion in the thickness direction of each portion divided into 10 equal portions, the crystalline structure among the 10 locations measured. It means the number of points judged as . When the crystalline layer exists in the above position, it becomes possible to realize even better coating film adhesion.

In addition, it is preferable that the number of detection locations of the crystalline layer is five or less in order from the outermost surface portion to the thickness direction, including the outermost surface portion of the coating layer. By setting the number of detection points to 5 or less, it becomes possible to achieve both corrosion resistance and coating film adhesion more reliably.

In addition, it is preferable to measure the number of detection spots in the crystalline layer as described above at 3 arbitrary positions of the coating layer, and more preferably at 5 arbitrary positions of the coating layer.

The content of zirconium oxide contained in the coating layer is 1.0 mg/m ² to 10.0 mg/m ² per side in terms of metal Zr. When the content of zirconium oxide contained in the coating layer is 1.0 mg/m ² or more per side in terms of metal Zr, the barrier property by zirconium oxide is sufficient, and the yellowing blackening resistance to foods containing amino acids is good. The content per side of the zirconium oxide contained in the film layer is preferably 6.0 mg/m ² or more in terms of metal Zr. On the other hand, when the content of zirconium oxide contained in the coating layer exceeds 10.0 mg/m ² per side in terms of metal Zr, the coating film adhesion tends to decrease due to cohesive failure of the zirconium oxide itself. When the content of zirconium oxide contained in the coating layer is 10.0 mg/m ² or less per side in terms of metal Zr, it is possible to maintain excellent coating film adhesion. The content per side of the zirconium oxide contained in the film layer is preferably 8.0 mg/m ² or less in terms of metal Zr.

Here, the content of zirconium oxide in the coating layer is the content of zirconium oxide per single side. In addition, any element such as Fe, Ni, Cr, Ca, Na, Mg, Al, Si or the like may be contained in the coating layer in addition to the zirconium oxide described above. In addition, in the film layer, one type or two or more types of tin fluoride, tin oxide, tin phosphate, zirconium phosphate, calcium hydroxide, calcium, or a complex compound thereof may be contained. The content of zirconium oxide (amount of metal Zr) in the film layer is determined by dissolving a Sn-based plated steel sheet by immersing it in an acidic solution such as hydrofluoric acid and sulfuric acid, and chemical analysis such as ICP emission spectrometry for the obtained solution. to the measured value. Alternatively, the content of zirconium oxide (amount of metal Zr) may be obtained by X-ray fluorescence measurement.

<About the formation method of the coating layer>

Below, the formation method of the coating layer containing zirconium oxide is demonstrated.

The film layer containing zirconium oxide can be formed on the surface of the Sn-based plating layer by immersing a Sn-based plated steel sheet in an aqueous solution containing zirconium ions and subjecting the Sn-based plated steel sheet to a cathode electrolytic treatment. Surface cleaning by forced charge transfer by cathodic electrolytic treatment and hydrogen generation at the steel plate interface, together with the effect of promoting adhesion by raising the pH, is combined to form a film layer containing zirconium oxide on the Sn-based plated steel sheet. can

Here, in order for zirconium oxide of an amorphous structure to be formed in the film, it is necessary to increase the rate of precipitation of zirconium oxide on the Sn plating surface and to increase the rate of nucleation rather than crystal growth. For this purpose, after forming Sn-based plating on the surface of the steel sheet, or after forming a Sn-based plating layer, heat-melting treatment by heating to 231.9 ° C. or higher, which is the melting point of Sn, hardness WH (calcium concentration (ppm) × 2.5 + Magnesium concentration (ppm) × 4.1) is immersed in cooling water in the range of 100 ppm or more and 300 ppm or less, and then immersed the Sn-based plated steel sheet in an aqueous solution containing zirconium ions, using the Sn-based plated steel sheet as a cathode to obtain a predetermined It is necessary to conduct cathodic electrolytic treatment in the current density range.

By setting the hardness of the cooling water within the above range, a compound containing either or both of calcium and magnesium adheres to the Sn-based plating surface and acts as a nucleus during subsequent zirconium film deposition, thereby finely precipitating zirconium oxide, An amorphous structure of zirconium oxide is formed. Here, when the hardness WH of the cooling water exceeds 300 ppm, the compound containing either or both of calcium and magnesium excessively adheres to and aggregates on the Sn-based plating surface, so that zirconium oxide is unevenly and locally generated, It grows, and zirconium oxide of an amorphous structure is not obtained. The hardness WH of the cooling water is preferably 250 ppm or less. When the hardness WH of the cooling water is 250 ppm or less, zirconium oxide is more uniformly generated. On the other hand, when the hardness WH of the cooling water is less than 100 ppm, since there are few nucleation origins at the time of zirconium oxide precipitation, zirconium oxide is generated starting from non-uniform portions on the Sn-based plating surface, resulting in coarse zirconium oxide, resulting in an amorphous structure of zirconium oxide is not formed. The hardness WH of the cooling water is preferably 150 ppm or more.

It is preferable that the immersion time to cooling water is 0.5 second - 5.0 second. When the immersion time in the cooling water is less than 0.5 seconds, adhesion of the compound containing either or both of calcium and magnesium to the Sn-based plating surface becomes insufficient, making it difficult to obtain zirconium oxide with an amorphous structure. On the other hand, when the immersion time in the cooling water exceeds 5.0 seconds, the compound containing either or both of calcium and magnesium excessively adheres to and aggregates on the Sn-based plating surface, so that zirconium oxide is unevenly and locally. It is difficult to obtain zirconium oxide with an amorphous structure because it is generated and grown gradually.

Moreover, it is preferable that the temperature of cooling water is 10 degreeC - 80 degreeC. When the temperature of the cooling water is less than 10° C., adhesion of the compound containing either or both of calcium and magnesium to the Sn-based plating surface becomes insufficient, making it difficult to obtain zirconium oxide with an amorphous structure. On the other hand, when the temperature of the cooling water exceeds 80 ° C, the compound containing either or both of calcium and magnesium excessively adheres to and aggregates on the Sn-based plating surface, so that zirconium oxide is unevenly and locally generated, It grows, and it is difficult to obtain zirconium oxide with an amorphous structure.

Further, the interval from the end of the cooling water immersion treatment to the start of the next cathodic electrolytic treatment is preferably within 10 seconds, and more preferably within 5 seconds.

It is preferable to set the current density at the time of cathodic electrolytic treatment to 2.0 A/dm ² to 10.0 A/dm ² . When the current density is less than 2.0 A/dm ² , the formation rate of zirconium oxide is slow, and it is difficult to obtain zirconium oxide having an amorphous structure. This is because when the current density is less than 2.0 A/dm ² , hydrogen generation from the surface of the Sn-based plated steel sheet is small, so the precipitation rate of zirconium oxide is also slow, and zirconium and oxygen atoms are sufficiently diffused in the process of forming zirconium oxide to form stable crystals. It is thought that this is because it can form a lattice. On the other hand, when the current density exceeds 10.0 A/dm ² , since hydrogen generation from the surface of the Sn-based coated steel sheet becomes active and the pH in the vicinity of the steel sheet surface is increased to the vicinity of the treatment liquid, zirconium oxide is generated in the treatment liquid. Then, the resulting zirconium oxide becomes larger until it adheres to the surface of the steel sheet, making it difficult to obtain a zirconium oxide having an amorphous structure, and the thickness of the zirconium film becomes thick and the appearance deteriorates.

In addition, in order to form zirconium oxide having a crystalline structure on the upper layer of zirconium oxide having an amorphous structure, a Sn-based plated steel sheet having zirconium oxide having an amorphous structure is formed by cathodic electrolysis in an electrolytic treatment solution containing zirconium ions. After that, electrolytic treatment may be performed at a low current density. Specifically, after forming zirconium with an amorphous structure by cathodic electrolytic treatment at a current density of 2.0 A/dm ² to 10.0 A/dm ² , cathodic electrolytic treatment at a current density of less than 1.0 A/dm ² You can do it.

The concentration of zirconium ions in the cathode electrolyte may be appropriately adjusted according to production equipment, production rate (capacity), and the like. For example, it is preferable that zirconium ion concentration is 1000 ppm or more and 4000 ppm or less. In addition, there is no problem at all even if other components such as fluorine ions, phosphate ions, ammonium ions, nitrate ions, sulfate ions, and chloride ions are contained in the solution containing zirconium ions. As a source of zirconium ions in the cathode electrolyte, for example, a zirconium complex such as H ₂ ZrF ₆ can be used. Zr in the Zr complex described above becomes Zr ⁴⁺ due to an increase in pH at the interface of the cathode electrode and exists in the cathode electrolyte. These Zr ions also react in the cathode electrolyte to form zirconium oxide.

In addition, as a solvent of the cathode electrolyte solution at the time of cathode electrolytic treatment, water, such as distilled water, can be used, for example. However, the solvent is not limited to water such as distilled water, and can be appropriately selected depending on the substance to be dissolved, the method of formation, and the like.

Here, it is preferable that the liquid temperature of the cathode electrolyte during the cathode electrolytic treatment is in the range of, for example, 5°C to 50°C. By carrying out cathodic electrolysis at 50° C. or less, it is possible to form a dense and uniform structure of a coating layer formed of very fine particles. On the other hand, when the liquid temperature is less than 5°C, there is a possibility that the film formation efficiency is lowered. When the liquid temperature exceeds 50°C, the formed film is non-uniform, and defects, cracks, microcracks, etc. occur, making it difficult to form a dense film and becoming a starting point of corrosion.

In addition, the pH of the cathode electrolyte is preferably set to 3.5 to 4.3. If the pH is less than 3.5, the deposition efficiency of the Zr film is low, and if the pH is more than 4.3, zirconium oxide precipitates in the liquid, resulting in a coarse and rough Zr film.

In addition, in order to adjust the pH of the cathode electrolyte or to increase the electrolytic efficiency, for example, nitric acid or aqueous ammonia may be added to the cathode electrolyte.

In addition, at the time of formation of the said film layer, the time of cathode electrolytic treatment is not considered. What is necessary is just to adjust the time of cathode electrolytic treatment suitably according to the current density with respect to content of zirconium oxide (amount of metal Zr) in a target film layer. In addition, the conduction pattern at the time of cathodic electrolytic treatment may be continuous conduction or intermittent conduction.

In the above, the Sn-based plated steel sheet according to the present embodiment and the manufacturing method thereof have been described in detail.

Example

Next, while exemplifying Examples and Comparative Examples, the method for manufacturing the Sn-based coated steel sheet and the Sn-based coated steel sheet according to the present invention will be described in detail. In addition, the examples presented below are only examples of the method for manufacturing the Sn-based coated steel sheet and the Sn-based coated steel sheet according to the present invention, and the manufacturing method for the Sn-based coated steel sheet and the Sn-based coated steel sheet according to the present invention. This is not limited to the following examples.

<Method of manufacturing test material>

The manufacturing method of the test material is explained. In addition, the test material of each case mentioned later was manufactured according to the manufacturing method of this test material.

First, with respect to a low-carbon cold-rolled steel sheet with a sheet thickness of 0.2 mm, as a pretreatment, electrolytic alkali degreasing, water washing, dilute sulfuric acid immersion pickling, and water washing are performed, followed by electrolytic Sn-based plating using a phenolsulfonic acid bath, and then heating and melting processing was done. As a result, Sn-based plating layers were formed on both surfaces of the steel sheet subjected to these treatments. The amount of deposition of the Sn-based plating layer was about 2.8 g/m ² as a standard in terms of the amount of metal Sn per side. The amount of deposition of the Sn-based plating layer was adjusted by changing the energization time. In addition, the said heat-melting process was not performed about some test materials.

Next, the steel sheet on which the Sn-based plating layer was formed was immersed in cooling water having a predetermined hardness for a predetermined time. Within 5 seconds after that, cathode electrolytic treatment in an aqueous solution (cathode electrolyte) containing zirconium fluoride was started on the plated steel sheet that had undergone the immersion treatment, and a coating layer containing zirconium oxide was formed on the surface of the Sn-based plating layer. The liquid temperature of the cathode electrolyte is set to 35° C., the pH of the cathode electrolyte is adjusted to be 3.0 to 5.0, and the current density and cathode electrolysis treatment time are adjusted to the target content of zirconium oxide in the coating layer (amount of metal Zr). ) was appropriately adjusted according to. In the case of performing the cathode electrolytic treatment twice, the second cathode electrolytic treatment was performed immediately after the first cathode electrolytic treatment was finished and the setting of the current density was changed.

The Sn-based plated steel sheet produced in this way was subjected to various evaluations shown below.

[Adhesion amount per side of Sn-based plating layer (amount of metal Sn in Sn-based plating layer)]

The amount of adhesion per side of the Sn-based plating layer (amount of metal Sn in the Sn-based plating layer) was measured as follows. A test piece of a steel sheet having a plurality of Sn-based plating layers having a known metal Sn content was prepared. Next, for each test piece, the fluorescence X-ray intensity derived from metal Sn was measured in advance from the surface of the Sn-based plating layer of the test piece using a fluorescence X-ray analyzer (ZSX Primus manufactured by Rigaku Co., Ltd.). Then, a calibration curve showing the relationship between the measured fluorescence X-ray intensity and the amount of metal Sn was prepared. Then, with respect to the Sn-based plated steel sheet to be measured, the film layer was removed to prepare a test piece in which the Sn-based plated layer was exposed. The intensity of fluorescence X-rays derived from metal Sn was measured with a fluorescence X-ray apparatus on the surface where the Sn-based plating layer was exposed. The amount of adhesion per side of the Sn-based plating layer (that is, the content of metal Sn) was calculated by using the obtained fluorescence X-ray intensity and a calibration curve prepared in advance.

In addition, measurement conditions were made into X-ray source Rh, tube voltage of 50 kV, tube current of 60 mA, spectroscopic crystal LiF1, and measurement diameter of 30 mm.

[Investigation of the structure of the coating layer]

In order to investigate the structure of the film layer, a sample for TEM observation was prepared with FIB (Quata 3D FEG manufactured by FEI), and the prepared sample was subjected to TEM (manufactured by Nippon Electronics, electrolytic emission type transmission electron microscope JEM-2100F), After observing an arbitrary field of view at an accelerating voltage of 200 kV and a magnification of 100,000, the electron diffraction pattern of the film layer was examined at a beam diameter of 1 nm. In the obtained electron beam diffraction pattern, when a ring-shaped continuous diffraction pattern is obtained instead of a clear diffraction spot, it is judged to be an amorphous structure, and a total of 30 spots of 10 random spots in the film thickness direction are determined at 3 positions on the surface of the film layer. Among the measurements, the ratio of the location where the amorphous structure was obtained was defined as the amorphous structure ratio.

Amorphous structure ratio (%) = (Number of sites where amorphous structure was obtained/30) × 100

In addition, the case where a clear diffraction spot is obtained in the electron beam diffraction pattern is judged to be a crystalline structure, and the case where a crystalline structure is confirmed on the surface layer side of the coating layer at all three positions is regarded as an upper layer of zirconium oxide having an amorphous structure. , it was determined that a crystalline layer made of zirconium oxide having a crystalline structure was present.

In addition, in each of three arbitrary positions of the coating layer, the coating layer was divided into 10 equal portions in the thickness direction, and in the electron beam diffraction pattern of the central portion in the thickness direction of each portion divided into 10 equal parts, the number of locations judged to be crystalline structures among the measured 10 locations confirmed. The maximum value of the number of detected spots at 3 positions was taken as the number of detected spots in the crystalline layer.

[Content of Zirconium Oxide in Film Layer (Metal Zr Amount)]

The content of zirconium oxide (amount of metal Zr) in the coating layer was measured according to the method for measuring the amount of adhesion per side of the Sn-based plating layer (amount of metal Sn in the Sn-based plating layer). That is, a test piece of a Sn-based plated steel sheet to be measured was prepared. The intensity of fluorescent X-rays derived from metal Zr was measured for the surface of the coating layer of this test piece with a fluorescent X-ray analyzer (ZSX Primus manufactured by Rigaku Co., Ltd.). The content of zirconium oxide (amount of metal Zr) in the film layer was calculated by using the obtained fluorescence X-ray intensity and a calibration curve for metal Zr prepared in advance.

[Surface tone (yellowing) and yellowing over time]

The color tone (yellowing) of the surface was determined by the value of b* using a commercially available color difference meter SC-GV5 manufactured by Suga Instruments. The measurement conditions of b* are light source C, total reflection, and a measurement diameter of 30 mm. In addition, yellowing over time was tested by carrying out a wet test in which a test sample of a Sn-based coated steel sheet was placed in a constant temperature and humidity chamber maintained at 40 ° C. and a relative humidity of 80% for 4 weeks, and the color difference b* value before and after the wet test The amount of change Δb* of was obtained and evaluated.

If Δb* was 1 or less, it was evaluated as "A", if it was more than 1 and 2 or less, it was evaluated as "B", if it was more than 2 and 3 or less, it was evaluated as "C", and if it exceeded 3, it was evaluated as "NG". Evaluation "A", "B", and "C" were set as the pass.

[Coating Film Adhesion]

Coating film adhesion was evaluated as follows.

After the test material of the Sn-based coated steel sheet was subjected to a wet test by the method described in [Yellowing resistance], a commercially available epoxy resin paint for cans was applied to the surface at a dry weight of 7 g/m ² , and baked at 200° C. for 10 minutes, It was left at room temperature for 24 hours. Thereafter, with respect to the obtained Sn-based coated steel sheet, flaws reaching the surface of the steel sheet were placed in a checkerboard pattern (7 vertical and horizontal flaws at 3 mm intervals), and a tape peel test was conducted at the site using a commercially available adhesive tape to evaluate.

If the coating film at the area where the tape is applied is not peeled off at all, it is evaluated as “A”, and if peeling of the coating film is confirmed around the scratches of the grid, it is evaluated as “B”, and if peeling of the coating film is observed within the square of the grid grid, it is evaluated as “NG” did Evaluation "A" and "B" were made into the pass.

[Blackening resistance to yellowing]

The yellowing resistance to blackening was evaluated as follows.

A commercially available epoxy resin paint for cans was applied in a dry mass of 7 g/m ² to the test sample surface of the Sn-based coated steel sheet fabricated and wet tested by the method described in [Coating Film Adhesion], and then baked at 200° C. for 10 minutes, It was left at room temperature for 24 hours. Then, the obtained Sn-based plated steel sheet was cut into a predetermined size, immersed in an aqueous solution containing 0.3% sodium dihydrogenphosphate, 0.7% sodium hydrogenphosphate, and 0.6% L-cysteine hydrochloride, and heated to 121°C in a sealed container. - Retort treatment for 60 minutes was performed, and the appearance after the test was evaluated.

If no change in appearance was observed before and after the test, it was evaluated as "AA", if a slight (5% or less) blackening was observed, it was evaluated as "A", and if more than 5% and 10% or less of blackening was observed, it was evaluated as "B". And, when blackening was observed in more than 10% of the area of the test surface, it was evaluated as "NG". Evaluation "AA", "A", "B" was made into the pass.

[Corrosion resistance after painting]

Corrosion resistance after coating was evaluated as follows.

A commercially available epoxy resin paint for cans was applied in a dry mass of 7 g/m ² to the test sample surface of the Sn-based coated steel sheet fabricated and wet tested by the method described in [Coating Film Adhesion], and then baked at 200° C. for 10 minutes, It was left at room temperature for 24 hours. Thereafter, the obtained Sn-based plated steel sheet was cut into a predetermined size, and the presence or absence of rust after being immersed in commercially available tomato juice at 60°C for 7 days was visually evaluated.

If rust is not confirmed at all, it is evaluated as "AA", if rust is confirmed at an area ratio of 5% or less of the entire test surface, it is evaluated as "A", and if rust is observed at an area ratio of more than 5% and less than 10% of the entire test surface It was set as evaluation "B", and it was set as evaluation "NG" when rust was confirmed by the area ratio of more than 10% of the whole test surface. Evaluation "AA", "A", and "B" were made into the pass.

<Example 1>

Table 1 shows manufacturing conditions when the cooling water immersion conditions before forming zirconium oxide on the Sn plating layer and the formation conditions of zirconium oxide are changed. The Sn-based plating was produced from a known ferrostann bath by an electrolytic method, and the amount of current applied during electrolysis was changed so that the amount of Sn deposited per side was in the range of 0.2 g/m ² or more and 30.0 g/m ² . In addition, Table 2 shows various characteristics of the obtained Sn-based plated steel sheet and characteristic evaluation results. Here, in Table 2, content in terms of metal Sn of the Sn-based plating layer shown in Table 1 is reposted. In addition, in any test piece, it was confirmed by XPS that the zirconium contained in the film was each a zirconium oxide specified in the present invention.

As is clear from Table 2, the performances of a1 to a43 within the range of the present invention were good. On the other hand, it can be seen that the comparative examples b1 to b17 are inferior in at least one of yellowing resistance, coating film adhesion, yellowing blackening resistance, and corrosion resistance after coating.

As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to these examples. It is clear that those skilled in the art to which the present invention belongs can conceive of various changes or modifications within the scope of the technical idea described in the claims, and for these, of course, this invention It is understood that it falls within the technical scope of the invention.

Claims (3)

steel plate,
An Sn-based plating layer positioned on at least one side of the steel sheet;
The coating layer located on the Sn-based plating layer
Have,
The Sn-based plating layer contains 1.0 g/m ² to 15.0 g/m ² per side of Sn, in terms of metal Sn,
The coating layer contains zirconium oxide, and the content of the zirconium oxide is 1.0 mg/m ² to 10.0 mg/m ² per side in terms of metal Zr,
The zirconium oxide includes zirconium oxide having an amorphous structure,
Sn-based plated steel sheet, wherein a crystalline layer containing zirconium oxide having a crystalline structure as a main component exists on the upper layer of the zirconium oxide having an amorphous structure.
Here, in the electron beam diffraction pattern, a case where a clear diffraction spot is obtained is determined to be a crystalline structure, and a case where a ring-shaped continuous diffraction pattern is obtained instead of a clear diffraction spot is determined to be an amorphous structure. According to claim 1,
The crystalline layer in the coating layer includes the outermost surface portion of the coating layer, and
The Sn-based plated steel sheet according to claim 1 , wherein the number of detected locations of the crystalline layer is at least one or more in order from the outermost surface portion in the thickness direction.
Here, the outermost surface part means a part including the outermost surface of the film layer among the parts obtained by dividing the film layer into 10 parts in the thickness direction at an arbitrary position of the film layer,
The number of detection locations of the crystalline layer is determined by dividing the coating layer into 10 equal portions in the thickness direction at an arbitrary position of the coating layer, and in the electron beam diffraction pattern of the center portion in the thickness direction of each portion divided into 10 equal portions, the crystalline quality among the 10 locations measured. It means the number of points judged to be structures. According to claim 2,
The Sn-based plated steel sheet according to claim 1 , wherein the number of detection spots of the crystalline layer is five or less in order from the outermost surface portion in the thickness direction, including the outermost surface portion of the coating layer.